Two forested ridges in Aiea could become part of the growing zip line industry in Hawaii under a plan by a real estate development company for a site once eyed for residential development.

An affiliate of Towne Development of Hawaii Inc. has filed a draft environmental assessment with the state laying out plans for a zip line attraction in Waimalu above the existing Royal Summit neighborhood.

The estimated $1 million project would feature seven pairs of zip lines zigzagging between two ridges and providing rides for up to 25 groups a day on part of a 447-acre property, the assessment said.

Some area residents have expressed concern over increased traffic through their neighborhood generated by such a business.

Robert Young, a 30-year Royal Summit resident, expressed "great sadness" over Towne’s plan in written comments submitted to the developer.

"My wife and Ibought our home because of the quiet streets, nice neighbors, and we believed it would be a great place to raise our children," he said.

Towne said the zip line operation will have a relatively minor impact on traffic, will be unseen and unheard from neighboring properties, will eliminate a trespassing problem that has concerned neighbors, and will include a native plant restoration effort that benefits the environment.

"The proposed Waimalu Nature Park and Zipline Canopy Tour can achieve a low-impact economic use of the unique property,"the developer said in the assessment.

Towne projected that it would run an average of 15 tours a day and no more than 25 a day at the maximum.

Tour groups would be picked up at a collection point, possibly in Pearl City or Aiea, at hotels or other locations and brought to the property in vans. An estimated 66 van trips would be made per day, Towne said. The company also said customers won’t be allowed to drive or walk onto the property.

The operation will involve fencing off access and adding security that solves an existing problem of trespassing on the site. Towne estimates that 35 people a day go onto the property to hike; ride bicycles, motorcycles and ATVs; to hunt pigs; collect plants and flowers; and play paintball.

Towne said it will continue to allow Oahu Pig Hunters Association members access as long as there are no problems. The developer also said it will allow hiking by members of the Newtown Estates Community Association.

The company has teamed with three zip line operators on the project: Maui-based Flyin Hawaiian Zipline, Maui Zipline Co. and Ohio-based ZipZone Canopy Tours.

As part of the plan, Towne said it will remove invasive plant species that include strawberry guava and Koster’s curse, and increase native plant species.

"In the absence of some managed program, the status of native plants on the property will inevitably degrade, and the project could thus lead to a substantial overall net benefit for native flora," the environmental assessment said.

Towne’s project, if realized, would be the second zip line operation on Oahu and join a trend that has grown more rapidly on the neighbor islands largely as a tourist attraction. A third zip line on Oahu is also in the works at Kualoa Ranch.

Oahu’s one existing commercial zip line is a 400-foot-long ride from a tree over a miniature golf course at Bayview Golf Course. The seven Waimalu lines would range from 240 to 1,200 feet in length.

Chris Lau, executive vice president of Towne, said Oahu appears underserved by the popular attractions. "What we’re looking for is other activities for tourists,"he said.

According to a 2012 report by the state auditor, the first zip line course in the nation was built in Hawaii in 2002 and has hosted more than 250,000 riders over a decade.

The audit cited Attractions and Activities Association of Hawaii statistics that there were 22 known zip line tour operations in the state in 2012, with most of them on Maui and Hawaii island.

The audit estimated that more than 700,000 people a year take zip line rides in Hawaii, and that it is a lucrative business.

Based on common advertised prices — which the audit said range from $30 to $200 per ride — annual industry revenue in Hawaii could be $21 million to $140 million.

Towne bought the Waimalu site in 2005 for $800,000 from Tobu Department Store Co., which foreclosed on another Japanese company that had intended to rezone the land to develop about 300 house lots and a golf course.

Towne, a company primarily involved in housing development, said in the environmental assessment that it doesn’t consider residential use a prudent alternative.

The land is zoned for conservation use, which allows nature parks. Towne said it plans to include a nature center in a 1,200-square-foot building leading up to the zip lines, and give customers talks about the ecosystem during the two-hour tours.

Among permits needed by Towne is a conservation district use permit from the Department of Land and Natural Resources. If the permitting is granted without problems, Towne projects that it could begin construction by midyear and be finished six months later.